JP2006256336A - Shrinkable sheet material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shrinkable sheet material which can be formed by an inflation method excellent in productivity and which can provide a high shrinkage ratio even if the working is performed at comparatively low temperature. <P>SOLUTION: The shrinkable sheet material comprises a layer consisting primarily of a polyolefin based resin, and a layer consisting primarily of a polylactic acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable sheet-like material (film or sheet), and more particularly to a shrinkable sheet-like material used for shrink-wrapping containers and the like.

  Conventionally, a polyvinyl chloride (PVC) film has been mainly used as a material for shrink wrapping and shrink tying wrapping, but various materials other than PVC have been studied from the viewpoint of environmental problems. Therefore, a slightly flexible polyolefin resin shrink film has come to be used for shrink wrapping such as lunch boxes and side dishes sold at convenience stores.

Polyolefin resin shrink film is a desirable material because it has relatively few problems with endocrine disrupting chemicals, which are combustion-generated gases and so-called environmental hormones. It is difficult to increase the shrinkage rate. That is, in order to increase the shrinkage rate of the shrink film of polyolefin resin, it is necessary to use, for example, a cross-linked resin or an elastomer with strong rubber elasticity, which increases the material cost. Further, if the inflation method is used, mass productivity is excellent, but since it is necessary to increase the stretching temperature, it is necessary to increase the contraction temperature in order to obtain a predetermined contraction rate. On the other hand, when shrink-wrapping or shrink-binding a package that is sensitive to high temperatures, it is necessary to perform a low-temperature shrinking process at 60 to 120 ° C. Therefore, in order to achieve a high shrinkage rate at a relatively low temperature, tenter stretching or the like with high equipment costs or tubular stretching or the like with low productivity is currently used.
Therefore, there is a demand for a shrinkable film or sheet that has a high productivity and a low equipment cost, and that can obtain a high shrinkage rate even at a low temperature by using an inflation method.

  That is, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a shrinkable sheet-like material that can obtain a high shrinkage rate at a relatively low temperature by an inflation method excellent in productivity. It is in.

  The shrinkable sheet material of the present invention is a shrinkable sheet material having a layer mainly composed of a polyolefin-based resin and a layer mainly composed of polylactic acid.

In the present invention, the outermost layer is a layer mainly composed of a polyolefin resin, and at least one layer mainly composed of polylactic acid can be provided between the layers mainly composed of the polyolefin resin.
Further, an adhesive layer can be provided between the layer mainly composed of polyolefin resin and the layer mainly composed of polylactic acid.

Here, the adhesive layer may be a layer mainly composed of an acrylic-modified polyethylene resin.
The adhesive layer may be a layer mainly composed of an ethylene / epoxy / alkyl acrylate copolymer.
The polyolefin resin may be a linear low density polyethylene resin or an ethylene copolymer.

According to the present invention, by laminating a layer mainly composed of a polyolefin-based resin and a layer mainly composed of polylactic acid, that is, materials that have never been thought of to be combined so far By combining them, it was possible to obtain a flexible shrinkable sheet-like material having a high shrinkage rate at a relatively low temperature and improved breaking strength while utilizing an inflation method excellent in productivity.
Polylactic acid is a material that is biodegradable and does not cause environmental problems, and its stretched film and sheet have characteristics close to those of stretched PET, and have been studied for various uses. However, polylactic acid emphasizes only the biodegradable characteristics, and attention to the biodegradability is not so much, so far, the combination with a general resin has not been studied at all. However, polylactic acid, which has been expensive in the past, can be obtained at a price close to that of general-purpose resins thanks to mass production. Therefore, the present inventor has paid attention to characteristics other than biodegradability of polylactic acid and continued research on whether it is possible to develop a resin or a laminate that makes use of such characteristics and the characteristics of general resins, thereby completing the present invention. It came to let you. The completion of the present invention has greatly expanded the range of material selection and has contributed to the expansion of the field of material design.

  According to the present invention, it is possible to obtain a sheet-like material having a shrinkability equivalent to that of a conventional shrinkable sheet or film by using an inflation method excellent in mass productivity, and to provide an industrially extremely useful technique. I was able to.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.
The shrinkable sheet material of the present invention has at least one layer containing a polyolefin resin as a main component and at least one layer containing polylactic acid as a main component.
In consideration of the packaging machine suitability of the sheet-like material, water resistance, and the like, it is preferable that the outermost layers on the front surface and the back surface have layers mainly composed of a polyolefin resin. Here, the suitability of a sheet-like product for packaging machinery means that when the sheet-like product is passed through the packaging machine, the sliding property between the belt-like parts of the packaging machine and the surface of the sheet-like product is good, and the stretched film is shrunk. It means that it has excellent heat resistance when passing through the shrink tunnel used in the above. For polyolefin-based resins, know-how such as what kind of mixed materials should be selected and how to use additives should be established to satisfy not only these characteristics but also various characteristics. It is easy to select materials and prescriptions suitable for packaging machines. Therefore, it is convenient to make the required packaging machine suitability easily by making the layers mainly composed of polyolefin resin as both outer layers.

  In the present invention, the sheet-like material refers to a sheet or a film. As defined in JIS, a sheet is a thin product that is generally thin and has a thickness that is small compared to the length and width. A film is extremely small compared to the length and width, and has a maximum thickness. An arbitrarily limited thin flat product, usually supplied in the form of a roll (JIS K 6900). Therefore, it can be said that a particularly thin sheet is a film. However, since the boundary between the sheet and the film is not clear and difficult to distinguish clearly, as described above, the term “sheet-like material” is used as a concept including both the sheet and the film.

The polylactic acid used in the present invention is, for example, a polymer mainly composed of L-lactic acid, D-lactic acid or DL-lactic acid unit, or a mixture of these polymers. -For lactic acid, D-lactic acid can be copolymerized, and for D-lactic acid, L-lactic acid) can be copolymerized. The polylactic acid may contain other hydroxycarboxylic acid or the like as a small amount of a copolymer component, and may contain a small amount of a chain extender residue.
Monomers such as copolymerization components copolymerized with polylactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2- Examples thereof include bifunctional aliphatic hydroxycarboxylic acids such as hydroxy-3-methylbutyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone, and valerolactone.

  In the present invention, a known method such as a condensation polymerization method or a ring-opening polymerization method can be employed as the polymerization method. For example, in the condensation polymerization method, polylactic acid having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid, DL-lactic acid or the like. In the ring-opening polymerization method (lactide method), a polylactic acid-based polymer can be obtained by appropriately selecting and using a polymerization regulator, a catalyst, and the like as needed for lactide, which is a cyclic dimer of lactic acid. it can.

  The weight average molecular weight (Mw) of the polylactic acid used in the present invention is preferably in the range of 60,000 to 700,000, more preferably 80,000 to 400,000, and particularly preferably 100,000 to 300,000. If the weight average molecular weight of the polylactic acid-based polymer is 60,000 or more, practical mechanical properties and heat resistance can be exhibited. If the weight average molecular weight is 700,000 or less, the melt viscosity becomes high. It is not too inferior in moldability.

A layer containing polylactic acid as a main component may contain a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment, etc. for the purpose of adjusting various physical properties. it can. Furthermore, the adhesiveness and the like can be improved by performing corona treatment on the surface of the sheet-like material.
Various additives such as slip agents, antioxidants, plasticizers and impact modifiers are added to the polylactic acid-based layer, and polymer blends that improve strength and elongation are selected. be able to.

As the polylactic acid used in the present invention, for example, trade name “EcoPLA” (manufactured by Cargill, USA) can also be obtained commercially.
The thickness of the layer mainly composed of polylactic acid is not particularly limited, but is preferably in the range of 2 to 50 μm in the present invention.

Examples of the polyolefin resin used in the present invention include low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, and ethylene / methyl acrylate copolymer. And their copolymers, blends, cross-linked products, and the like, but the present invention is not limited thereto. The type of polyolefin resin can be appropriately selected according to the characteristics required for the shrinkable sheet material. For example, when the strength of the sheet material is important, a linear low density polyethylene resin is used. When importance is attached to the adhesiveness and heat-fusibility of the sheet-like material, it is preferable to select an ethylene copolymer such as an ethylene / vinyl acetate copolymer or acrylic-modified polyethylene.
In the present invention, an appropriate amount of various additives such as an antioxidant, a slip agent and an antifogging agent can be added to the polyolefin resin as necessary.
The thickness of the layer mainly composed of polyolefin resin is not particularly limited, but is preferably in the range of 2 to 50 μm, for example.

  In the present invention, in addition to the above layers, an adhesive layer, an intermediate layer, a reproduction layer, and the like can be provided as necessary. For example, when the adhesive strength between each layer is insufficient, an adhesive layer can be formed, and an adhesive layer is provided between a layer mainly composed of polyolefin resin and a layer mainly composed of polylactic acid. Can be formed. In the present invention, the outermost layer has a layer mainly composed of a polyolefin-based resin, the layer mainly composed of polylactic acid (middle layer) is interposed between the layers, and the outermost layer and the middle layer are between Each has a structure having an adhesive layer, that is, a layer structure of at least five layers of outermost layer / adhesive layer / middle layer / adhesive layer / outermost layer. Of course, it may have a layer structure of five or more layers.

  As the adhesive used for the adhesive layer, vinyl-based, acrylic-based, polyamide-based, polyester-based, rubber-based, polyurethane-based adhesives and the like can be generally used, but biodegradable adhesives such as starch, Polysaccharides such as amylose and amylopectin, proteins such as glue, gelatin, casein, zein, collagen, and polypeptides, unvulcanized natural rubber, aliphatic polyester, and the like can also be used.

In the present invention, an adhesive made of an acrylic-modified polyethylene resin is preferable. For example, an ethylene / ethyl acrylate copolymer, an ethylene / methyl methacrylate copolymer, an ethylene / acrylic acid copolymer, an ethylene / methacrylic acid copolymer, etc. The higher the acrylic modification ratio, the better. In the present invention, it is particularly desirable to use an ethylene / epoxy / alkyl acrylate copolymer as an adhesive because a sufficient interlayer adhesion can be obtained.
The thickness of the adhesive layer is not particularly limited, but is preferably in the range of about 1 to 3 μm.

  In the present invention, the thickness ratio of each layer constituting the shrink sheet is not particularly limited, but the thickness of the layer mainly composed of polylactic acid in the total thickness of the shrink sheet is approximately A range of 25% to 60% is preferable. If it is 25% or more, a sufficient shrinkage can be obtained, and if it is 60% or less, the film will not be broken in the normal use range.

  The shrinkable sheet-like material of the present invention can be manufactured based on a manufacturing method by a general inflation method, but it is desirable that the final valve diameter with respect to the die diameter is 5 times or more, that is, the blow-up ratio is 5 times or more. . If the blow-up ratio is less than 5 times, a sufficient shrinkage rate in the lateral direction may not be obtained.

  The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
As a polyolefin resin, an ethylene / methacrylic acid copolymer (EMAA) manufactured by Mitsui DuPont Polychemical Co., Ltd. There is a polylactic acid having a weight average molecular weight of about 200,000, the thickness of the layer (A) containing polyolefin resin as the main component is 6 μm, and the thickness of the layer (C) containing polylactic acid as the main component is 6 μm. A shrinkable sheet-like material having a total thickness of 12 μm having a layer constitution of a layer (A) containing a polyolefin resin as a main component / a layer (C) containing a polylactic acid as a main component was produced by an inflation method. The temperature was 190 ° C. and the blow-up ratio was 6 times.

Example 2
Example 1 is the same as Example 1 except that the thickness of the layer mainly composed of polyolefin resin, the thickness of the layer mainly composed of polylactic acid, and the layer configuration are changed as shown in Table 1. Thus, a shrink sheet having a total thickness of 12 μm was produced.

Example 3
In Example 1, the type of polyolefin resin, the thickness of the layer mainly composed of polyolefin resin and the thickness of the layer mainly composed of polylactic acid were changed as shown in Table 1, As shown in the layer structure, a shrinkable sheet-like material was prepared in the same manner as in Example 1 except that a layer formed from EMAA was further formed to have a thickness of 1.5 μm as an adhesive layer or an intermediate layer (B).

Example 4
In Example 1, the type of polyolefin resin, the thickness of the layer mainly composed of polyolefin resin and the thickness of the layer mainly composed of polylactic acid were changed as shown in Table 1, As shown in the layer structure, as an adhesive layer or intermediate layer (B), it is formed from the trade name “Bond First 7N” (manufactured by Sumitomo Chemical Co., Ltd.) which is a polyethylene / glycidyl methacrylate / methyl acrylate copolymer (PE / GMA / MA). A shrinkable sheet was produced in the same manner as in Example 1 except that the layer to be formed was formed to have a thickness of 1.5 μm.

Comparative Example 1
In Example 1, as shown in Table 1, the type of polyolefin resin and the thickness of the layer containing the polyolefin resin as the main component were changed, and the polylactic acid was used as the main component as shown in Table 1. In the same manner as in Example 1 except that a layer formed from PE / GMA / MA is provided as an adhesive layer or an intermediate layer so as to have a thickness of 6 μm, a shrinkable sheet shape having a total thickness of 12 μm is not provided. The thing was produced.

Reference Example As shown in Table 1, a commercially available shrink sheet of polyolefin resin by tubular stretching was prepared for reference.

  The shrinkage ratios of the obtained shrinkable sheet-like materials of Examples 1 to 4, Comparative Example 1, and Reference Example were measured. That is, the shrinkable sheet was immersed in an oil bath kept constant at a temperature of 120 ° C. for 10 seconds, and the shrinkage in the machine direction (MD) and the transverse direction (TD) were measured. In addition, if MD shrinkage is 30% or more and TD shrinkage is 40% or more, there is no practical problem. The obtained results are shown in Table 1.

  As is apparent from Table 1, Examples 1 to 4 can be produced by the inflation method, and the shrinkage in the MD direction and the TD direction are the same as those of the commercial products listed as reference examples even at a temperature of 120 ° C. It was found to have a shrinkage ratio of

  On the other hand, the shrinkable sheet-like material of Comparative Example 1 could not be put to practical use and could not be made into a sheet-like material having a sufficient shrinkage rate. Moreover, about the shrinkable sheet material of Examples 1-4, when various physical properties, such as slipperiness, heat resistance, and intensity | strength, were evaluated, about the shrinkable sheet material of Example 1, Example 2 and 3, it was adhesive. The shrinkable sheet-like material of Example 4 is excellent in heat-fusibility, and is excellent in strength. Thus, by appropriately selecting the type of polyolefin resin, desired properties can be obtained. It was found that it can be easily added. In addition, although the shrink sheet-like thing only of the layer which consists of polylactic acid was formed by the inflation method, the fracture strength was weak and it was an impractical shrink sheet-like thing.

Claims (6)

  A shrinkable sheet-like material comprising a layer composed mainly of a polyolefin-based resin and a layer mainly composed of polylactic acid.   The outermost layer is a layer mainly composed of a polyolefin-based resin, and has at least one layer composed mainly of polylactic acid between the layers mainly composed of the polyolefin-based resin. The shrinkable sheet-like material as described.   The shrinkable sheet-like material according to claim 1, further comprising an adhesive layer between a layer mainly composed of a polyolefin-based resin and a layer mainly composed of polylactic acid.   The shrinkable sheet-like article according to claim 3, wherein the adhesive layer is a layer mainly composed of an acrylic-modified polyethylene resin.   The shrinkable sheet material according to claim 3, wherein the adhesive layer is a layer mainly composed of an ethylene / epoxy / alkyl acrylate copolymer.   The shrinkable sheet-like product according to any one of claims 1 to 5, wherein the polyolefin resin is a linear low density polyethylene resin or an ethylene copolymer.